direct3d 11 tutorial: tessellation -...
TRANSCRIPT
Direct3D Tutorial: Tessellation 3/31/20102
Overview of Direct3D tessellation
Design of Hull and Domain Shaders
–Two simple examples
How to write efficient tessellation code
–An advanced example
Topics Covered in This Session
Direct3D Tutorial: Tessellation 3/31/20103
Compact representation
Real-time, continuous level of detail
Better looking silhouettes
Direct rendering of high-order surfaces created by modeling software
Faster – Animations can be done on the lower resolution mesh
There are many really good reasons for using tessellation
Direct3D Tutorial: Tessellation 3/31/20104
.. and one really bad reason for using it.
Tessellating unnecessarily!
–Triangles not seen
–Triangles too small
Direct3D Tutorial: Tessellation 3/31/20105
Direct3D 11 Tessellator Stages
Direct3D Tutorial: Tessellation 3/31/20106
Hull Shader
Control point phase
–Runs once per control point
Patch constant phase
–Runs once per input primitive
–Returns tessellation factors
Direct3D 11 Tessellator Stages
Direct3D Tutorial: Tessellation 3/31/20107
Tessellator Stage
Generates the new vertices
Higher tessellation factors mean more triangles generated.
Direct3D 11 Tessellator Stages
Level 1.0 Level 1.5 Level 3.0
Direct3D Tutorial: Tessellation 3/31/20108
Domain Shader
Runs once per vertex for surface evaluation at each vertex
Vertex data passed in as parametric coordinates
Direct3D 11 Tessellator Stages
Direct3D Tutorial: Tessellation 3/31/20109
A simple example of tessellation (part 1)
HULL SHADER
TESSELLATOR
Triangle Patch Mesh
Tessellated Mesh
Direct3D Tutorial: Tessellation 3/31/201010
A simple example of tessellation (part 2)
DOMAINSHADER
Tessellated Mesh
Displaced Mesh
Displacement Map
Direct3D Tutorial: Tessellation 3/31/201011
A simple example of tessellation (part 3)
PIXELSHADER
Displaced Mesh
Final Image
Diffuse Texture Normal Map
Direct3D Tutorial: Tessellation 3/31/201012
// set the shaders – note the addition of hull and domain shaders
pd3dImmediateContext->VSSetShader( g_pTessellationVS, NULL, 0 );
pd3dImmediateContext->HSSetShader( g_pTessellationHS, NULL, 0);
pd3dImmediateContext->DSSetShader( g_pTessellationDS, NULL, 0);
pd3dImmediateContext->GSSetShader( NULL, NULL, 0 );
Pd3dImmediateContext->PSSetShader( g_pSimplePS, NULL, 0 );
// set the vertex buffer which contains the triangle patches
UINT stride = sizeof(Vertex);
UINT offset = 0;
pd3dImmediateContext->IASetVertexBuffers( 0, 1, &g_pMeshVB, &stride,
&offset );
// set input layout
pd3dImmediateContext->IASetInputLayout( g_pVertexLayout );
// set the primitive topology – note the topology is a control point
// patch list, which enables tessellated drawing
pd3dImmediateContext->IASetPrimitiveTopology(
D3D11_PRIMITIVE_TOPOLOGY_3_CONTROL_POINT_PATCHLIST);
// Draw the model – same as drawing without tessellation
pd3dImmediateContext->Draw( g_SceneModel.triCount * 3, 0 );
C++ Code (part 1)
Direct3D Tutorial: Tessellation 3/31/201013
Simple Hull Shader (control point phase)// Called once per control point
[domain("tri")] // indicates a triangle patch (3 verts)
[partitioning("fractional_odd")] // fractional avoids popping
// vertex ordering for the output triangles
[outputtopology("triangle_cw")] [outputcontrolpoints(3)]
// name of the patch constant hull shader
[patchconstantfunc("ConstantsHS")]
[maxtessfactor(7.0)] //hint to the driver – the lower the better
// Pass in the input patch and an index for the control point
HS_CONTROL_POINT_OUTPUT HS( InputPatch<VS_OUTPUT_HS_INPUT, 3>
inputPatch, uint uCPID : SV_OutputControlPointID )
{
HS_CONTROL_POINT_OUTPUT Out;
// Copy inputs to outputs – “pass through” shaders are optimal
Out.vWorldPos = inputPatch[uCPID].vPosWS.xyz;
Out.vTexCoord = inputPatch[uCPID].vTexCoord;
Out.vNormal = inputPatch[uCPID].vNormal;
Out.vLightTS = inputPatch[uCPID].vLightTS;
return Out;
}
Direct3D Tutorial: Tessellation 3/31/201014
Simple Hull Shader (patch constant phase)
//Called once per patch. The patch and an index to the patch (patch
// ID) are passed in
HS_CONSTANT_DATA_OUTPUT ConstantsHS( InputPatch<VS_OUTPUT_HS_INPUT, 3>
p, uint PatchID : SV_PrimitiveID )
{
HS_CONSTANT_DATA_OUTPUT Out;
// Assign tessellation factors – in this case use a global
// tessellation factor for all edges and the inside. These are
// constant for the whole mesh.
Out.Edges[0] = g_TessellationFactor;
Out.Edges[1] = g_TessellationFactor;
Out.Edges[2] = g_TessellationFactor;
Out.Inside = g_TessellationFactor;
return Out;
}
Direct3D Tutorial: Tessellation 3/31/201015
Simple Domain Shader (part 1)// Called once per tessellated vertex
[domain("tri")] // indicates that triangle patches were used// The original patch is passed in, along with the vertex position in barycentric
coordinates, and the patch constant phase hull shader output (tessellation factors)
DS_VS_OUTPUT_PS_INPUT DS( HS_CONSTANT_DATA_OUTPUT input,
float3 BarycentricCoordinates : SV_DomainLocation,
const OutputPatch<HS_CONTROL_POINT_OUTPUT, 3>
TrianglePatch )
{
DS_VS_OUTPUT_PS_INPUT Out;
// Interpolate world space position with barycentric coordinates
float3 vWorldPos =
BarycentricCoordinates.x * TrianglePatch[0].vWorldPos +
BarycentricCoordinates.y * TrianglePatch[1].vWorldPos +
BarycentricCoordinates.z * TrianglePatch[2].vWorldPos;
// Interpolate texture coordinates with barycentric coordinates
Out.vTexCoord =
BarycentricCoordinates.x * TrianglePatch[0].vTexCoord + ...
// Interpolate normal with barycentric coordinates
float3 vNormal =
BarycentricCoordinates.x * TrianglePatch[0].vNormal + ...
// Interpolate light vector with barycentric coordinates
Out.vLightTS =
BarycentricCoordinates.x * TrianglePatch[0].vLightTS + ...
Direct3D Tutorial: Tessellation 3/31/201016
Simple Domain Shader (part 2)
// sample the displacement map for the magnitude of displacement
float fDisplacement = g_DisplacementMap.SampleLevel(
g_sampleLinear, Out.vTexCoord.xy, 0 ).r;
fDisplacement *= g_Scale;
fDisplacement += g_Bias;
float3 vDirection = -vNormal; // direction is opposite normal
// translate the position
vWorldPos += vDirection * fDisplacement;
// transform to clip space
Out.vPosCS = mul( float4( vWorldPos.xyz, 1.0 ),
g_mWorldViewProjection );
return Out;
} // end of domain shader
Direct3D Tutorial: Tessellation 3/31/201017
Simple Pixel Shader
float4 PS( DS_VS_OUTPUT_PS_INPUT i ) : SV_TARGET
{
float3 vLight;
float3 vNormal;
// Get the normal
vNormal = normalize( (g_NormalMap.Sample(
g_sampleLinear, i.vTexCoord ).rgb) * 2 - 1 );
vLight = normalize(i.vLightTS);
// get base color
float4 vBaseColor = float4(g_BaseMap.Sample( g_sampleLinear,
i.vTexCoord).rgb, 1.0);
// light the pixel
float diffuse = saturate( dot( vNormal, vLight ) );
float4 color = (vBaseColor * diffuse) + (vBaseColor *
g_vAmbientColor);
return color;
}
Direct3D Tutorial: Tessellation 3/31/201018
Demo: Simple Tessellation
Direct3D Tutorial: Tessellation 3/31/201019
Simple but powerful
– A few hours of coding but can be used for something as useful as terrain rendering
Minimal work in the Hull Shader
– Driver recognizes the “Pass Through” shader and optimizes for it
Normal Map Lighting
– Lighting a displaced surface can be difficult because the normals change!
– Normal map lighting avoids this since normal map is paired with the displacement map:
Some things to remember about this example
Direct3D Tutorial: Tessellation 3/31/201020
Hardware tessellation can be used to render 3D parametric surfaces directly
Cubic Bezier surfaces are easy to render
– Can convert many types of surfaces to Bezier patches in the Hull Shader
Domain Shader evaluates the surface at the vertex
Parametric Surfaces
Direct3D Tutorial: Tessellation 3/31/201021
Bicubic Bezier Patch Example
HULL SHADER
TESSELLATORDOMAINSHADER
Pos(u,v) = S S Bm(u) Bn(v) G
Where: B0 = (1-t)3 P00 P01 P02 P03
B1 = 3t(1-t)2 and G = P10 P11 P12 P13
B2 = 3t2(1-t) P20 P21 P22 P23
B3 = t3 P30 P31 P32 P33
m = 0 n = 0
33
Bezier Control Points
Tessellated Bezier Patch
Direct3D Tutorial: Tessellation 3/31/201022
Bezier Patch C++ Code
// Layout for control points
const D3D11_INPUT_ELEMENT_DESC patchlayout[] =
{
{"POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0,
D3D11_INPUT_PER_VERTEX_DATA, 0 },
};
// ...
// Control points are stored in the vertex buffer
pd3dImmediateContext->IASetVertexBuffers(0,1,&g_pControlPointVB,
&Stride, &Offset );
// Primitive Topology – note 16 control points this time
pd3dImmediateContext->IASetPrimitiveTopology(
D3D11_PRIMITIVE_TOPOLOGY_16_CONTROL_POINT_PATCHLIST );
// Draw the mesh
pd3dImmediateContext->Draw( g_vertexCount, 0 );
Direct3D Tutorial: Tessellation 3/31/201023
Bezier Patch Domain Shader Helper functions (part 1)
//Evaluates the Bernstein basis for a given parameter t
float4 BernsteinBasis(float t)
{
float invT = 1.0f - t;
return float4( invT * invT * invT, // (1-t)3
3.0f * t * invT * invT, // 3t(1-t)2
3.0f * t * t * invT, // 3t2(1-t)
t * t * t ); // t3
}
// Derivative of the basis functions for computing tangents
float4 dBernsteinBasis(float t)
{
float invT = 1.0f - t;
return float4( -3 * invT * invT, // -3(1-t)2
3 * invT * invT - 6 * t * invT, // 3(1-t)-6t(1-t)
6 * t * invT - 3 * t * t, // 6t(1-t) – 3t2
3 * t * t ); // 3t2
}
Direct3D Tutorial: Tessellation 3/31/201024
Bezier Patch Domain Shader Helper functions (part 2)float3 EvaluateBezier( const OutputPatch<HS_OUTPUT, OUTPUT_PATCH_SIZE>
bezpatch, float4 BasisU, float4 BasisV )
{
// This function essentially does this: Value(u,v) = S S Bm(u) Bn(v) G
float3 Value = float3(0,0,0);
Value = BasisV.x * ( bezpatch[0].vPosition * BasisU.x +
bezpatch[1].vPosition * BasisU.y + bezpatch[2].vPosition *
BasisU.z + bezpatch[3].vPosition * BasisU.w );
Value += BasisV.y * ( bezpatch[4].vPosition * BasisU.x +
bezpatch[5].vPosition * BasisU.y + bezpatch[6].vPosition *
BasisU.z + bezpatch[7].vPosition * BasisU.w );
Value += BasisV.z * ( bezpatch[8].vPosition * BasisU.x +
bezpatch[9].vPosition * BasisU.y + bezpatch[10].vPosition *
BasisU.z + bezpatch[11].vPosition * BasisU.w );
Value += BasisV.w * ( bezpatch[12].vPosition * BasisU.x +
bezpatch[13].vPosition * BasisU.y + bezpatch[14].vPosition *
BasisU.z + bezpatch[15].vPosition * BasisU.w );
return Value;
}
Direct3D Tutorial: Tessellation 3/31/201025
Bezier Patch Domain Shader[domain("quad")] // indicates that the patches are quads
DS_OUTPUT BezierDS( HS_CONSTANT_DATA_OUTPUT input,
// Since this is a quad, tessellated vertex positions are given with
// two (u,v) parameters
float2 UV : SV_DomainLocation,
const OutputPatch<HS_OUTPUT, OUTPUT_PATCH_SIZE> bezpatch )
{ // Evaluate the basis functions at (u, v)
float4 BasisU = BernsteinBasis( UV.x );
float4 BasisV = BernsteinBasis( UV.y );
float4 dBasisU = dBernsteinBasis( UV.x );
float4 dBasisV = dBernsteinBasis( UV.y );
// Evaluate the surface position for this vertex
float3 WorldPos = EvaluateBezier( bezpatch, BasisU, BasisV );
// Evaluate the tangent space for this vertex (using derivatives)
float3 Tangent = EvaluateBezier( bezpatch, dBasisU, BasisV );
float3 BiTangent = EvaluateBezier( bezpatch, BasisU, dBasisV );
float3 Norm = normalize( cross( Tangent, BiTangent ) );
DS_OUTPUT Output;
Output.vPosition = mul( float4(WorldPos,1), g_mViewProjection );
Output.vWorldPos = WorldPos;
Output.vNormal = Norm;
return Output;
}
Direct3D Tutorial: Tessellation 3/31/201026
Bezier Patch Demo
Direct3D Tutorial: Tessellation 3/31/201027
Apply a displacement decal to any mesh, then draw with tessellation to accurately render the displacement
Tessellates arbitrary scene meshes without modifications to the art pipeline
Use the hull shader to control tessellation levels and improve performance
Advanced Tessellation Example: Decal Tessellation
Direct3D Tutorial: Tessellation 3/31/201028
Store hit location tangent space into a constant buffer
Ray cast to find the hit location
Normal Binormal Tangent Position
N0 B0 T0 P0
N1 B1 T1 P1
N2 B2 T2 P2
Direct3D Tutorial: Tessellation 3/31/201029
Compute the displacement map coordinates in the Domain Shader
For each tessellated
vertex, project it’s
position onto the plane
formed by the hit
location and its tangent
space.
Direct3D Tutorial: Tessellation 3/31/201030
Decal Tessellation Domain Shader (part 1)
// See if this vertex is affected by any of the decals
for (int i = 0; i < MAX_DECALS; i++)
{
// get the hit location
float3 vHitLocation = g_HitLocation[i];
// find the distance from the current vertex to the hit location
float distanceToHit = distance(vWorldPos, vHitLocation.xyz);
// check if the vertex is within the decal radius
if (distanceToHit <= decalRadius)
{
// translate the position to a coordinate space
// with the hit location as the origin
float3 vWorldPosTrans = vWorldPos - vHitLocation.xyz;
// create the decal tangent space matrix
float3x3 mWorldToTangent = float3x3( g_vTangent[i].xyz,
g_vBinormal[i].xyz, g_vNormal[i].xyz );
Direct3D Tutorial: Tessellation 3/31/201031
Decal Tessellation Domain Shader (part 2)
// Transform the position into decal tangent space to
// get the displacement map texture coordinate.
float3 vWorldPosTrans = vWorldPos - vHitLocation.xyz;
float3 vDMTexCoord = mul( mWorldToTangent,vWorldPosTrans);
// normalize coordinate to values between 0 and 1
vDMTexCoord /= decalRadius* 2;
vDMTexCoord += 0.5;
// project displacement map coordinate onto the x,y plane
vDMTexCoord.z = 1; // z = 0 tells pixel shader this is invalid
// sample the displacement map
float fDisplacement = g_DisplacementMap.SampleLevel(
g_sampleLinear, vDMTexCoord.xy, 0 ).r;
fDisplacement *= g_Scale;
fDisplacement += g_Bias;
// hit direction is opposite of tangent space normal
float3 vDirection = -g_vNormal[i].xyz;
Direct3D Tutorial: Tessellation 3/31/201032
Decal Tessellation Domain Shader (part 3)
// Displace the vertex
vWorldPos += vDirection * fDisplacement;
// Create the light vector
float3 vLightWS = g_vLightPosition.xyz - vWorldPos;
// transform the light vector into tangent space
Out.vLightTS = mul( mWorldToTangent, vLightWS );
// Use the displacement map coord for the normal map coord
Out.vNMTexCoord = vDMTexCoord;
break;
} // end of “if (distanceToHit <= decalRadius)”
} // end of “for (int i = 0; i < MAX_DECALS; i++)”
Out.vPosCS = mul( float4( vWorldPos.xyz, 1.0 ),
g_mWorldViewProjection );
return Out;
} // end of domain shader
Direct3D Tutorial: Tessellation 3/31/201033
Decal Tessellation Pixel Shader
// Get the Normal and Light vectors for lighting
// If vNMTexCoord.z = 1, then this pixel is part of the decal
if (i.vNMTexCoord.z < 1)
{
// Not part of the decal, just use the interpolated normal.
vNormal = normalize(i.vNormal);
vLight = normalize(i.vLightWS);
}
else
{
// Part of the decal, get the normal from the decal normal map.
vNormal = normalize( (g_NormalMap.Sample( g_sampleLinear,
i.vNMTexCoord ).rgb) * 2 - 1 );
vLight = normalize(i.vLightTS);
}
...
Direct3D Tutorial: Tessellation 3/31/201034
Demo: Decal Tessellation
Direct3D Tutorial: Tessellation 3/31/201035
Analysis
– Expensive Domain Shader
– Small triangles are inefficient
Hardware wants triangles to be at least 8 pixels
Solution
– Reduce the number of tessellated vertices
Fewer executions of the Domain Shader
– Hull Shader can adjust the tessellation factors
Making it faster
Direct3D Tutorial: Tessellation 3/31/201036
Adjust the tessellation factors globally for the object based on distance
Simple LERP done outside of shader code:
TF = (1 – t) maxTF + t
where: t = distance / maxTessellationDistance
Or, use Hull Shader to calculate screen space edge length
Use an impostor when far away (just normal map)
Distance Adaptive Tessellation
Direct3D Tutorial: Tessellation 3/31/201037
Distance Adaptive Tessellation Demo (1)
Distance adaptive up close: 33 FPS
Direct3D Tutorial: Tessellation 3/31/201038
Distance Adaptive Tessellation Demo (2)
Distance adaptive far away: 2054 FPS!
Direct3D Tutorial: Tessellation 3/31/201039
Two orders of magnitude improvement for when object is far away!
Doesn’t help much for objects close up
Very little code changes
Distance Adaptive Results
Direct3D Tutorial: Tessellation 3/31/201040
Use the displacement map to determine how much to tessellate
High frequency of displacements (jagged) require more tessellation
Low Frequency of displacements (smooth) require fewer tessellation
Displacement Adaptive
Direct3D Tutorial: Tessellation 3/31/201041
Displacement Adaptive with Decal Tessellation (1)
Patch TriangleDecal
Decal
See if the given edge
needs to be tessellatedFirst check if either
endpoint is within
the radius of the
decal
Direct3D Tutorial: Tessellation 3/31/201042
Displacement Adaptive with Decal Tessellation (2)
Patch Triangle
Decal
See if the given edge
needs to be tessellated
If neither endpoint is
within the decal
radius, check to the
distance from the
decal to the edge.
Direct3D Tutorial: Tessellation 3/31/201043
Displacement Adaptive with Decal Tessellation (3)
Patch Triangle
See if the inside of the triangle
needs to be tessellated by seeing if
the distance from the hit location to
the triangle plane is within the decal
radius.
Direct3D Tutorial: Tessellation 3/31/201044
Displacement Adaptive Hull Shader Pseudo Code
for (each decal in the list){
if ( either vertex of Edge 0 is within the decal’s radius){
tessellate this edge;}else{
if ( (distance from the decal to Edge 0 is within the radius) && (decal intersects the line segment) )
{tessellate this edge;
}}
Do the same for Edge 1 and Edge 2 …
if ( any edge is tessellated ) || ( ( distance from decal to triangle plane is within radius)
&& ( decal projected onto triangle plane is within triangle) ){
tessellate the inside}
}
Direct3D Tutorial: Tessellation 3/31/201045
Displacement Adaptive Hull Shader (part 1)
// default tessellation factors
Out.Edges[0] = Out.Edges[1] = Out.Edges[2] = Out.Inside = 1;
// Iterate over all decals to see if tessellation is needed
for (int i = 0; i < MAX_DECALS; i++)
{
edgeTessellated = false;
float3 vDecalLocation = g_DecalLocation[i];
// Edge 0
vDecalToPos0 = vDecalLocation - vPos0;
magSquared0 = dot( vDecalToPos0 , vDecalToPos0 );
vDecalToPos1 = vDecalLocation - vPos1;
magSquared1 = dot( vDecalToPos1, vDecalToPos1 );
// See if the distance to either vertex < decal radius
if ((magSquared0 <= decalRadiusSquared) ||
(magSquared1 <= decalRadiusSquared))
{
Out.Edges[0] = g_TessellationFactor;
edgeTessellated = true;
}
Direct3D Tutorial: Tessellation 3/31/201046
Displacement Adaptive Hull Shader (part 2)
else
{
// project line onto triangle patch edge
vEdge0 = vPos1 – vPos0;
magSquaredEdge0 = dot(vEdge0, vEdge0);
vProjected = (dot(vDecalPos0,vEdge0)/magSquaredEdge0) * vEdge0;
magSquaredProj = dot(vProjected, vProjected);
// Use the Pythagorean theorem to find the squared distance.
distanceSquared = magSquared0 - magSquaredProj;
if ((distanceSquared <= decalRadiusSquared) && // within radius
(dot(vProjected,vEdge0) >= 0) && // within edge line segment
(magSquaredProj <= magSquaredEdge0))
{
Out.Edges[0] = g_tessellationFactor;
edgeTessellated = true;
}
}
// Do the same thing for Edge 1 and Edge 2 ...
Direct3D Tutorial: Tessellation 3/31/201047
Displacement Adaptive Hull Shader (part 3)// Inside
float3 vPlaneNormal = normalize( cross(vEdge0, -vEdge2) );
// Use the dot product to find distance between point and plane
float distanceToPlane = abs (dot(vPlaneNormal, vDecalToPos0));
if (distanceToPlane <= decalRadius)
{
// Point in triangle test using barycentric coordinates
float dotAA = dot(vEdgeA, vEdgeA);
float dotAB = dot(vEdgeA, vEdgeB);
float dotBB = dot(vEdgeB, vEdgeB);
float invDenom = 1.0 / (dotAA * dotBB - dotAB * dotAB);
float dotAHit = dot(vEdgeA, vHitEdge0);
float dotBHit = dot(vEdgeB, vHitEdge0);
float u = (dotBB * dotAHit - dotAB * dotBHit) * invDenom;
float v = (dotAA * dotBHit - dotAB * dotAHit) * invDenom;
if ( ((u > 0) && (v > 0) && ((u + v) < 1)) || edgeTessellated )
{
Out.Inside = tessellationFactor;
}
}
} // end of for loop
Direct3D Tutorial: Tessellation 3/31/201048
Displacement Adaptive Tessellation Demo (1)
Displacement adaptive up close: 1434 FPS!
Direct3D Tutorial: Tessellation 3/31/201049
Displacement Adaptive Tessellation Demo (2)
Wireframe view showing tessellation only on affected patches
Direct3D Tutorial: Tessellation 3/31/201050
Two orders of magnitude improvement in performance when object is close to camera!
Combined with Distance Adaptive, almost as fast as without tessellation when viewed from far away.
But wait there’s more …
Displacement Adaptive Results
Direct3D Tutorial: Tessellation 3/31/201051
Why tessellate (or even draw) triangles facing away from the camera that you can’t see?
Do back-face culling in the Hull Shader
Patches are not drawn if all of the tessellation factors are set to zero.
Back-Face Culling
Direct3D Tutorial: Tessellation 3/31/201052
Back-Face Culling in the Hull Shader
// find two triangle patch edges
float3 vEdge0 = vPos1 - vPos0;
float3 vEdge2 = vPos2 - vPos0;
// Create the normal and view vector
float3 vFaceNormal = normalize( cross(vEdge2,vEdge0) );
float3 vView = normalize( vPos0 - g_vEyePosition );
// A negative dot product means facing away from view direction.
// Use a small epsilon to avoid popping, since displaced vertices
// may still be visible with dot product = 0.
if ( dot(vView, vFaceNormal) < -0.25 )
{
// Cull the triangle by setting the tessellation factors to 0.
Out.Edges[0] = 0;
Out.Edges[1] = 0;
Out.Edges[2] = 0;
Out.Inside = 0;
return Out; // early exit
}
Direct3D Tutorial: Tessellation 3/31/201053
Back-Face Culling Demo (1)
Wireframe view with back face culling
Direct3D Tutorial: Tessellation 3/31/201054
Back-Face Culling Demo (2)
Rotated wireframe view with back face culling showing culled patches
Direct3D Tutorial: Tessellation 3/31/201055
About 40% improvement when one decal is culled.
Easy to implement – only a few lines of code
Make cull test with a small epsilon to avoid popping
Back-Face Culling Results
Direct3D Tutorial: Tessellation 3/31/201056
Frustum Culling
Group tessellated draw call together
Orientation Adaptive Tessellation
– Use dot(V, N) to find silhouette patches
Hull Shader
– Try to reduce data passed in and out
Domain Shader
– Try to move work to Pixel Shader
– Reduce data passed out
Geometry Shader
– Use Stream Out to avoid re-tessellating an object
Other Optimizations to Consider
Direct3D Tutorial: Tessellation 3/31/201057
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